Sources of Parental Germplasm
Walter R. Fehr and Walter P. Suza
Readings:
- Chapter 10: Parent Selection [pdf], Principles of Cultivar Development. Vol. 1: Theory and Technique, by Walter R. Fehr (Access the full book)
- Chapter 11: Plant Introduction and Genetic Diversity [pdf], Principles of Cultivar Development. Vol. 1: Theory and Technique, by Walter R. Fehr
Introduction
The first step in the development of any cultivar is obtaining a segregating population in which to do selection. In most cases, the breeder develops the segregation population by crossing parents that have the potential of producing progeny with the traits desired in the new cultivar. The purpose of this lesson is to understand the sources of parent germplasm that a breeder may choose to use.
Sources of Parents
Cultivars and elite breeding lines
The primary source of parent germplasm is elite cultivars and experimental breeding lines. Crosses among elite parents have the best chance of providing offspring that are superior to the parents and that will be useful as new cultivars.
The breeder of a plant species often will want to access elite cultivars and breeding lines from other breeders in private companies or public institutions. It is extremely important that a breeder have written permission to use germplasm developed by someone else and that the signed document be retained, in case any question is raised about the method by which the germplasm was received.
A verbal agreement is not sufficient when accessing parent germplasm from another breeder for several reasons.
- The individual may not realize that they do not have the authority to make the verbal agreement.
- The terms of a verbal agreement may be forgotten.
- The individual with whom the verbal agreement is made may leave the company or institution.
- The exchange of germplasm has become more restricted for both private and public institutions.
If an institution decides to restrict its exchange of parent germplasm, it may want to see a written document that verifies that germplasm previously received from it was properly obtained by another breeder. There are cases in which use of parent germplasm from another breeder without written permission has resulted in the loss of a job and legal awards of millions of dollars.
The terms of a written agreement vary among private and public institutions. The material transfer agreement at (Figure 1) from the Iowa State University Research Foundation at Ames, IA, is only one example of terms that may be involved in the exchange of parent germplasm.
Plant introductions
Plant introductions (PIs) in the United States are managed by the National Genetic Resources Program (NGRP). The NGRP is responsible for the acquisition, characterization, preservation, documentation, and distribution of germplasm acquired from other countries or from breeding programs in the United States. The description of available plant germplasm and the method to acquire it can be found at www.ars-grin.gov.
Plant introductions have been a valuable source of novel genes for important traits for breeding programs. These include genes for insect resistance, disease resistance, seed quality, and many other traits. It common for breeders to evaluate plant introductions when searching for a trait that is not available in elite cultivars or breeding lines.
At the present time, plant introductions acquired through NGRP are available without a charge. Persons who obtain plant introductions are asked to provide the results of their evaluation to NGRP for the benefit of others who may be interested in the trait sometime in the future.
Review Questions
- The purpose of this question is to help you understand the types of parents that are used in cultivar development. For each of the following cultivars listed in the January 2011 issue of the Journal of Plant Registrations, list the cultivar name, the species, and the parents crossed to form the population used for selection. Indicate whether the parents were cultivars, experimental lines, or plant introductions.
To properly make answer this question, you must understand the symbolism that is used in the articles.
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- A cultivar is denoted with apostrophes around the name, if the author does not specifically use the word “cultivar” before the name. For example, the cultivar Pella would be designated in an article as ‘Pella’, if the author did not say “cultivar Pella’. An experimental line, such as A38, would not have apostrophes around its name.
- Cultivars deposited in the NPGS are given a PI designation that is indicated in parentheses after the cultivar name, such as ‘Pella’ (PI123456). PIs that are not cultivars would not have a cultivar name associated with them.
- A parent designated as a brand can be considered a cultivar for the purposes of this assignment. The distinction between a cultivar and a brand will be discussed in Agron. 521.
- For some plant species, breeders designate the ancestry of a population, in addition to the immediate parents. The system is described in Crop Science 8: 405-406 (1968). The key point is that the immediate parents of a cross are located on either side of the single /. Those are the parents you should include in your answer.
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- Dan barley – JPR 5: 1-4 (2011):
- Awesome Kentucky bluegrass – JPR 5: 5-10 (2011):
- Au Red Ace red clover – JPR 5: 11-13 (2011):
- Essex lentil – JPR 5: 19-21 (2011):
- Aloha seashore paspalum – JPR 5: 22-26 (2011):
- Bailey barley – JPR 5: 27-39 (2011):
- Intercross ryegrass – JPR 5: 40-44 (2011):
- Nelson annual ryegrass – JPR 5: 45-48 (2011):
- UA 4910 soybean – JPR 5: 49-53 (2011):
- Barlow wheat – JPR 5: 62-67 (2011):
- Merl wheat – JPR 5: 68-74 (2011):
- Snowglenn wheat – JPR 5: 81-86 (2011):
- Snowmass wheat – JPR 5: 87-90 (2011):
- SW049029104 wheat – JPR 5: 91-97 (2011):
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- Based on your survey in question 1, what percentage of the parents were cultivars, experimental lines, and plant introductions? What would explain the percentages that you obtained?
- For a plant species of your choice, identify a plant introduction that you could acquire from the National Plant Germplasm System at www.ars-grin.gov. Provide the number of the PI that you have chosen and the rationale for your choice based on the traits you would like to obtain from the PI. Describe where the PI was acquired, where it is maintained in the United States, and how you would order it.
Cultivated varieties that are well-suited to the typical environmental conditions of the target production area. These cultivars possess the necessary alleles for key traits such as end-use quality, agronomic performance, disease resistance, and regional adaptation.
A line developed from the cross of selected parental lines, resulting in F1 plants. The F1 plants are allowed to intermate over time to produce offspring with stable, pure-breeding lines. The pure-breeding (experimental) lines are used for evaluating specific traits, testing genetic hypotheses, and forming the basis for developing new cultivars.
Plants within a species that have the same genetic composition and are genetically pure, (i.e., inbred line). Lines are typically experimental, not agronomically competitive (hence not commercially available), and are used only in plant breeding.
The acquisition and distribution of germplasm from one country to another.
